In the development of electrical systems, designers must carefully consider a variety of factors that can negatively affect the performance of signal transmission over high-speed serial links on printed circuit boards. Among such factors are signal crosstalk, stubs, physical dimensions, material properties, and impedance. Particularly problematic are signal reflections, which can occur at various locations along a high-speed serial link. Reflected signals travel back on the serial link toward the transmitter of the signal, interfering with other signals traversing the serial link, and potentially reducing signal integrity of signals subsequently transmitted by the transmitter. Defects in the signals typically manifest as jitter and altered amplitude.
Although determining the cause and effect of signal reflections is often complicated, signal reflections often occur at an interface between dissimilar media (e.g., a connector pin contacting an electrical trace). The nature of the interface generally determines the nature of the signal reflection at the interface. For example, the amplitude and phase of a reflected signal depends upon any mismatch of impedances of the dissimilar media at the interface. Herein, such interfaces are generally referred to as impedance discontinuities. One solution to the problem of signal reflection is to minimize or eliminate impedance mismatches at an interface. However, it may be impractical to eliminate all potential causes of signal reflection along a high-speed serial link. Thus, there remains a need of another technique for reducing or eliminating the effects of signal reflection on serial links on printed circuit boards.